This is a CATV wiring scheme where all of the cable lines in the house meet at one central location, the junction.

Not all houses are wired this way. Some are wired as a loop system.

In the above picture, you can see the benefit of having a junction. Not only is the signal distributed more evenly among the house, but now no matter where you put the cable modem, you have great signal, and only one splitter to pass through.

This is obviously not a representation of the size and configuration of every house. Some houses only have on cable outlet, and I've been to one that had 17.

In cases like that where you have a large number of outlets, generally a reconfiguring of the splitters is in order. (More about this in my splitters section.)

Feedback received on this FAQ entry:

it's perfer all houses be in a home run system, all outlets are balance and your modem can have it's own line, if your house is not in that way, it's worth the investment, look up a local cable installer or let your provider do it